The present invention relates to a novel thread chaser for a conventional lathe which permits the cutting of threads in either the metric or American system of measurement.
Threads are generally measured by the U.S. standard or the metric standard. The existent dual system of measurement necessitates that a lathe be equipped to cut both U.S. standard and metric threads. Many lathes are now equipped to perform this function since they have a dual purpose gear box. However, dual cutting lathes still have only a single lead screw for the carriage which carries the cutting tool. Thus, it is very difficult to cut a metric thread with a U.S. standard lead screw since most threads must be repeatedly cut until a finsihed product is obtained. This entails returning the cutting tool to exactly the same cutting path of the prior cut.
The usual threading procedure now employed is to cause the half-nuts to engage the lead screw of the carriage and to begin the first cut. At the end of a threading pass the lathe is reversed without disengaging the half-nuts and returned to the starting position. The lathe is then restarted and the subsequent cut of the thread takes place. This process is repeated until a proper thread is obtained in the work piece. As may be surmised, this is a slow and tedious process. In certain cases cutting a metric thread in this manner is not possible. Specifically, where the work piece has a shoulder the lathe may not be stopped in time (because of inertia), to prevent the cutting tool from damaging the shoulder. The existent thread chasers only work where the lead screw and the cuts being performed on the work piece are multiples of each other.
There is a need for a thread chaser which may be used to accurately locate a cutting path for use on multiple cuts of a work piece where the lead screw of a lathe and the piece being cut are not necessarily threaded according to the same standard of measurement.